Fish populations in lakes: typical assemblages and levels of eutrophication

Abstract

Statistical analyses have been applied to the results of fish sampling operations on twenty French natural lakes (altitude < 1500 m); three fish assemblages were evidenced and placed inside the general evolution scheme of lakes. The oligo- and oligo-mésotrophic lakes can be characterized by Coregonids (inside a Coregonid ichtyo-region) or by the association of Alburnus alburnus - Gobio gobio, with the presence of Phoxinus phoxinus and Salmo trutta. Into mesotrophic lakes, the assemblage Esox lucius - Scardinius erythrophtalmus - Tinca tinca could be considered as typical, and is replaced by Stizostedion lucioperca - Gymnocephalus cernuus with large Cyprinids (Cyprinus carpio, Abramis brama) in eutrophic lakes. Because of the capacity of adaptation of the fish, these assemblages do not correspond narrowly to trophic quality indices but are indicators of the "ichtyological condition" of a lake, as requested by the European Water Frame Directive.